Diagnosis
Diagnostic criteria
True bimaxillary dentoalveolar protrusion can be diagnosed when the below criteria is met:
- Lip separation at rest of more than 4mm
- Excessive effort to bring the lips into closure
- Excessive incisor proclination and protrusion, beyond their racial norms
Measurements of excessive incisor proclination
- Qualitatively on facial appearance
- Angle between the upper and lower incisors (interincisal angle) is < 126 degrees (Eastman standards) for caucasians
- Upper incisor angulation relative to the cranial base (U1-SN) is > 112 degrees (Steiner analysis) for caucasians
- Lower incisor angulation relative to the mandibular plane (L1-MP) is > 102 degrees (Steiner analysis) for caucasians
Dental vs. skeletal
Bimaxillary dentoalveolar protrusion is by definition a protrusion dental condition that has an impact on the facial profile. Skeletal bimaxillary protrusion may also exist where both jaws are prognathic.
Clinical Considerations
The aetiology
- Dental protrusion occurs as an adaptation of the soft tissue pattern (Keating 1986)
- Large and fleshier lips, often present in black and asian populations, have less resting lingual forces against the teeth allowing for incisors to be proclined
High relapse risk
- There is a high relapse risk in the correction of bimaxillary dentoalveolar protrusion as the aetiology is often the patient’s soft tissue pattern (Keating 1986)
- Orthodontic retraction of the incisors without changing the soft tissue pattern will still lead to incisors proclining again into their neutral zone
- Spaces can reopen rapidly post-treatment as well (as such extractions in spaced dentitions should be cautioned) (Carter and Slattery 1988)
Should the bimaxillary dentoalveolar protrusion be corrected?
- Treatment decisions should be based on treatment indications
- A higher amount of incisor proclination and protrusion are normal for black and asian populations. As such, caucasian norms should not be used as an indicator of treatment for these patients.
Limitations of treatment
- High relapse risk
- Inadequate alveolar width for retraction (e.g. a narrow mandibular symphysis is a significant limitation to thee amount of incisor retraction)
